PCB3703 chapter 17
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Questions and Answers

What is the primary function of the ventral (anterior) root of the spinal cord?

  • Motor neuron transmission (correct)
  • Sensory information transmission
  • Supporting neuronal cell bodies
  • Reflex arc initiation
  • Which covering of a nerve surrounds the entire nerve structure?

  • Endoneurium
  • Perineurium
  • Myelin sheath
  • Epineurium (correct)
  • In which major ascending tract do signals related to fine touch and proprioception travel?

  • Anterior spinothalamic tract
  • Fasciculus gracilis and cuneatus (correct)
  • Lateral spinothalamic tract
  • Anterior spinocerebellar tract
  • What is the primary function of the Golgi tendon organ?

    <p>To inhibit muscle activity to prevent damage</p> Signup and view all the answers

    What type of information does the lateral spinothalamic tract carry?

    <p>Pain and temperature</p> Signup and view all the answers

    Which is NOT a characteristic of the crossed extensor reflex?

    <p>Promotes balance by extending muscles on the same side of the injury</p> Signup and view all the answers

    During which stage of spinal shock is there an absence of reflexes below the site of injury?

    <p>Initial areflexia</p> Signup and view all the answers

    What characterizes the decussation process of the anterior spinothalamic tract?

    <p>Decussates immediately upon entry</p> Signup and view all the answers

    What symptom is commonly associated with upper motor neuron damage as indicated by Babinski's sign?

    <p>Extension of the toes</p> Signup and view all the answers

    Which type of neuron is primarily involved in the somatic nervous system?

    <p>Upper motor neurons</p> Signup and view all the answers

    What happens to a patient who exhibits a Babinski's sign?

    <p>It indicates upper motor neuron damage</p> Signup and view all the answers

    What occurs during denervation supersensitivity after a spinal cord injury?

    <p>Hyperactive stretch and flexion reflexes return</p> Signup and view all the answers

    Which aspect of the spinal cord primarily conducts ascending traffic for sensory information?

    <p>Posterior columns</p> Signup and view all the answers

    What characteristic defines decerebrate rigidity?

    <p>Exaggerated extensor activity with hyperactive stretch reflexes</p> Signup and view all the answers

    Which of the following muscles are NOT activated during the withdrawal reflex?

    <p>Ipsilateral limb extensors</p> Signup and view all the answers

    What role do association neurons play in the spinal reflex pathways?

    <p>They facilitate communication between sensory and motor pathways</p> Signup and view all the answers

    What is the primary function of the pia mater in relation to the spinal cord?

    <p>Adheres directly to the spinal cord and contains CSF</p> Signup and view all the answers

    Which aspect of gray matter in the spinal cord is primarily responsible for processing sensory information?

    <p>Posterior horns</p> Signup and view all the answers

    In spinal cord anatomy, where does the conus medullaris typically terminate?

    <p>At the level of L2</p> Signup and view all the answers

    Which structure is known for containing cerebrospinal fluid (CSF) within the spinal cord?

    <p>Central canal</p> Signup and view all the answers

    Which spinal nerve roots are primarily responsible for conveying motor signals from the spinal cord to the body?

    <p>Ventral (anterior) roots</p> Signup and view all the answers

    Which type of spinal reflex involves an immediate withdrawal from a harmful stimulus?

    <p>Withdrawal reflex</p> Signup and view all the answers

    What is the primary clinical significance of Babinski’s sign?

    <p>Suggests possible upper motor neuron lesions</p> Signup and view all the answers

    Which structure separates the left and right halves of the spinal cord?

    <p>Anterior median fissure</p> Signup and view all the answers

    Study Notes

    Spinal Cord and Spinal Nerves Anatomy

    • The spinal cord is located within the vertebral canal of the vertebral column.
    • It's surrounded by cerebrospinal fluid (CSF), meninges, and vertebral bone.

    Meninges

    • Meninges are connective tissue membranes protecting the brain and spinal cord.
    • Dura mater is the outermost layer, dense, irregular connective tissue.
    •  The epidural space is located between the dura mater and the vertebral foramen, primarily composed of fat and connective tissue.
    • Arachnoid mater is the middle meninx, with delicate elastic and collagen fibers.
    • The subdural space exists between the dura and arachnoid mater, containing interstitial fluid.
    • Pia mater is a thin transparent layer that adheres to the spinal cord. It surrounds the subarachnoid space, which contains cerebrospinal fluid (CSF).

    External Spinal Cord Anatomy

    • The spinal cord extends from the medulla to L2.
    • There are cervical and lumbosacral enlargements supplying upper and lower appendages, respectively.
    • The conus medullaris is the tapered inferior end of the spinal cord.
    • Cauda equina are spinal nerves arising from the cord.
    •  The filum terminale is a pia mater extension.

    Spinal Nerves

    • The spinal cord has 31 pairs of spinal nerves.
    • They are named after their vertebral segment.
    • Spinal nerves have divisions: cranial (C1-C8), thoracic (T1-T12), lumbar (L1-L5), sacral (S1-S5), and coccygeal.

    Internal Spinal Cord Anatomy

    • Photomicrographs show light and dark matter.
    • Gray matter forms a butterfly-shaped core, while white matter surrounds it.
    • The spinal cord is divided into left and right halves by a posterior median sulcus and anterior median fissure.
    • Gray matter consists of anterior and posterior horns, and a gray commissure. It also has a central canal that contains CSF.
    • Neuron cell bodies are located within the spinal cord.

    White Matter

    • Myelinated motor and sensory fibers form columns in the white matter.
    • These columns include anterior, posterior, and lateral columns (funiculi).
    • Distinct bundles of nerve fibers comprise white matter tracts.

    Spinal Nerves Structure & Function

    • Spinal nerves connect the spinal cord to the body.
    • Spinal roots contain sensory and motor neurons.
    • Sensory nerves enter via dorsal roots, with cell bodies in the dorsal root ganglia.
    • Motor nerves exit via ventral roots, containing cell bodies in the gray matter of the cord.

    Nerve Plexuses

    • Cervical plexus (C1-C4)
    • Brachial plexus (C5-T1)
    • Lumbar plexus (T12-L4)
    • Sacral plexus (L4-S4)

    Nerve Coverings

    • Endoneurium surrounds nerve fibers.
    • Perineurium surrounds fascicles.
    • Epinurium surrounds the entire nerve.

    Spinal Cord Physiology

    • The spinal cord conducts nerve impulses (white matter) from receptors to the brain (ascending) and from the brain to effectors (descending).
    • Both routes decussate.
    • The spinal cord is the center for spinal reflexes (gray matter).

    Major Ascending Tracts

    • Fasciculus gracilis and cuneatus transmit proprioception, fine touch, pressure, and vibration.
    • Posterior spinocerebellar tract and anterior spinocerebellar tract transmit proprioception.
    • Lateral and anterior spinothalamic tracts transmit pain and temperature sensations.

    Major Descending Tracts

    • Descending tracts are primarily somatic motor.
    • Upper motor neurons are in the primary motor cortex, with axons extending to lower motor neurons.
    • Lower motor neurons are in brain stem or spinal cord, their axons extending to neuromuscular junctions.

    Autonomic Nervous System

    • The autonomic nervous system controls visceral functions.
    • Preganglionic neuron cell bodies are in the brainstem or spinal cord, with axons extending to postganglionic neurons (peripheral ganglia).
    • Postganglionic neurons then innervate the visceral effectors, such as smooth muscles, glands, and cardiac muscles.

    Pyramidal Tracts

    • Pyramidal/corticospinal tracts are responsible for precise, voluntary motor control of skeletal muscles.
    • This system starts in the motor cortex, decussates in the brainstem, and ends at anterior horns of the spinal cord.

    Extrapyramidal Tracts

    • Extrapyramidal tracts control subconscious motor activity, motor tone, posture, and coordination.
    • Involved tracts include rubrospinal, vestibulospinal, tectospinal, and reticulospinal.

    Motor Control

    • Motor control is integrated within the motor cortex, basal ganglia, and cerebellum.
    • These systems are intricately interconnected.

    Spinal Organization of Motor Function

    • Motor control ultimately relies on α-motor neurons that innervate skeletal muscles.
    • Variable motor unit sizes impact motor control.
    • Recruitment of motor units, along with temporal summation, regulate muscle force output.

    Sensory Input for Motor Control

    • Proprioceptive information is crucial for motor control, provided by muscle stretch receptors (e.g., muscle spindles) and Golgi tendon organs.
    • Muscle spindles and their associated intrafusal fibers provide signals about muscle length and rate of stretch.
    • Golgi tendon organs respond to stretch in tendons and affect muscle activity.

    Spinal Reflexes

    • Spinal reflexes are fast, predictable, and automatic responses to stimulation.
    • Different classifications exist based on the type of sensory and effector organs involved:
      • viscerovisceral,
      • viscerosomatic,
      • somatovisceral,
      • somatosomatic.
    • Reflex arcs involve receptors, sensory neurons, an integrating center (gray matter), motor neurons, and effectors (muscles).
    • Important spinal reflexes include the phasic stretch reflex, the tonic stretch reflex, the tendon reflex, and withdrawal and crossed extensor reflexes.

    Clinical Value of Reflex Evaluation

    • Reflex evaluations can assess anesthesia levels, intervertebral disc issues, and muscular disorders and weakness.

    Spinal Cord Transection

    • Spinal shock occurs after spinal cord injury and involves initial loss of reflexes below the injury.
    • Denervation supersensitivity and hyperreflexia follow later.

    Babinski's Sign

    • Babinski's sign is an abnormal plantar reflex, where the toes extend instead of flexing. It indicates upper motor neuron damage.

    Decerebrate Rigidity

    • Decerebrate rigidity is a condition characterized by exaggerated extensor muscle activity following brainstem injury.

    Postural Reflexes

    • Postural reflexes maintain balance during various activities.
    • Vestibulo-ocular, vestibular placing, and nystagmus reflexes are crucial types of postural responses.

    Locomotion

    • Spinal cord circuits control locomotion through rhythmic motor patterns.
    • Tonic activity in descending pathways and foot pressure modulate these patterns.

    Spinal Cord Anatomy and Physiology Summary

    • Spinal cord structure and function are tightly interwoven.
    • Understanding the intricate connections between receptors, nerves (sensory and motor), and effectors is critical to grasping how the nervous system maintains homeostasis and controls movement.

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